Hi there.

I'm Erfan - a full-stack Magento developer and consultant living in Perth, Australia. I'm the organiser of Western Australia's Magento meetup and at the moment I'm working at SPEQS, a startup that will revolutionise how people buy eyewear online.

For Magento 1, check out my post here: Four ways to edit Magento's Javascript.
A while ago I wrote a reasonably popular article that simply listed out the different ways you can modify Magento's Javascript. Here we go again, but for Magento 2.
Theme overwrite
Of course, the easiest way to modify Javascript...